Design and Development of Precision Miniature Twin-bladed Ultra High-speed Air Turbine

Research and development of this thesis is to investigate the performance and characteristics of precision miniature twin-bladed air turbines in an ultra-high-speed region. In order to improve the machining efficiency of ultra-precision and micro fabrication technology, a high speed spindle is essential for the miniature tools which widely applied in systems such as PCB drilling machines, micro fabrication machines, and dental handpieces, etc. To realize the performance in high speed region, the air driven turbine is verified to be more feasible than an electromagnetic actuator. Furthermore, the operational efficiency and quality of the high speed spindle are significantly influenced by the turbine impeller and its bearings, respectively.
Through detailed configuration studies and performance analyses on diverse miniature turbine impellers, the efficiency-influential and quality-influential parameters have been derived. And based on optimization results, a novel type of twin-bladed impeller (TB-impeller) on air turbine, which consists of two parallel impellers with an angular offset, is developed. The offset twin impellers can efficiently and smoothly transform pneumatic energy into rotational energy. Therefore, steady driving force and less dynamic unbalance are easily achieved for reducing operational disturbances such as vibration, noise, and wear.
By applying a finite element analytical method, the operational performance and quality of the new developed twin bladed impeller such as rotational speed, torque, vibration, and noise were analyzed for comprehending influences of the design parameters and the operational parameters. While the inlet diameter, the blade shape and its geometric parameters are the dominant design parameters; the inlet pressure ,mass flow rate, and the outlet pressure are the main operational parameters. Through the turbine impellers, the pneumatic energy can be transformed into operational energy in form of the flow field and the pressure distribution as well as the energy loss in form of turbulence.
Also by integrating knowledge of production technology, a neat design of the turbine impellers suitable for automatic manufacturing processes is developed. And furthermore, through an elaborate layout of the flow guiding, a minimum rotational run-out can be effectively achieved without any complicate and costly machining processes. Consequently, it can significantly depress the stream noise and raise the operation lifetime of bearings. According to our experimental verification at the same inlet pressure, the free running speed, power efficiency, and torque of novel TB-impeller are 10 %, 10 %, and 15 % higher than traditional counterparts, respectively. And the stream noise can be reduced by 17 %. The developed miniature spindle with novel TB-impeller can efficiently realize high speed rotation with high free running speed, high torque, less vibration, and less noise. By its superior features, the developed twin-bladed impeller also broadens the application possibilities in high speed machining fields with high efficiency and fewer expenses.